tidytuesday - NFL Data

library(tidyverse)
library(janitor)
library(readxl)
#library(tidylog)
library(skimr)
library(knitr)

This week’s tidytuesday data comes from Pro Football Reference and includes attendance, standings, and game stats for each game. Well do a quick EDA and generate a few ideas of what might be interesting to look at.

# Import the data from tidytuesday: https://github.com/rfordatascience/tidytuesday

attendance <- readr::read_csv('https://raw.githubusercontent.com/rfordatascience/tidytuesday/master/data/2020/2020-02-04/attendance.csv')
standings <- readr::read_csv('https://raw.githubusercontent.com/rfordatascience/tidytuesday/master/data/2020/2020-02-04/standings.csv')
games <- readr::read_csv('https://raw.githubusercontent.com/rfordatascience/tidytuesday/master/data/2020/2020-02-04/games.csv')

First, lets take a look at the data and see what it can tell us at face value.

The attendance dataset

kable(head(attendance))

team	team_name	year	total	home	away	week	weekly_attendance
Arizona	Cardinals	2000	893926	387475	506451	1	77434
Arizona	Cardinals	2000	893926	387475	506451	2	66009
Arizona	Cardinals	2000	893926	387475	506451	3	NA
Arizona	Cardinals	2000	893926	387475	506451	4	71801
Arizona	Cardinals	2000	893926	387475	506451	5	66985
Arizona	Cardinals	2000	893926	387475	506451	6	44296

attendance %>%
  skim()

Data summary
Name	Piped data
Number of rows	10846
Number of columns	8
_______________________
Column type frequency:
character	2
numeric	6
________________________
Group variables	None

Variable type: character

skim_variable	n_missing	complete_rate	min	max	empty	n_unique	whitespace
team	0	1	5	13	0	32	0
team_name	0	1	4	10	0	32	0

Variable type: numeric

skim_variable	n_missing	complete_rate	mean	sd	p0	p25	p50	p75	p100	hist
year	0	1.00	2009.53	5.75	2000	2005.0	2010	2015.00	2019	▇▇▇▇▇
total	0	1.00	1080910.03	72876.97	760644	1040509.0	1081090	1123230.00	1322087	▁▁▇▆▁
home	0	1.00	540455.01	66774.65	202687	504360.0	543185	578342.00	741775	▁▁▅▇▁
away	0	1.00	540455.01	25509.33	450295	524974.0	541757	557741.00	601655	▁▂▇▇▂
week	0	1.00	9.00	4.90	1	5.0	9	13.00	17	▇▆▆▆▇
weekly_attendance	638	0.94	67556.88	9022.02	23127	63245.5	68334	72544.75	105121	▁▁▇▃▁

We certainly have some interesting statistics here to mess with. It looks like the ‘total,’ ‘home,’ and ‘away’ attendance columns represent the entire season, while the ‘weekly_attendance’ field is for each week. Therefore, it looks like each row is a game. So there should be some variability in how many rows there are amongst the teams, as some make it to the playoff and some do not (therefore they’d have more games). A look at the summary statistics should tell us more… if that is the case or not.

So, as was expected, there does seem to be some variability associated with how many games they play. Not to worry, I’ll probably stay away from analyzing just that, and focus on either more aggregated descriptives or simply other statistics herein.

The standings dataset

kable(head(standings))

team	team_name	year	wins	loss	points_for	points_against	points_differential	margin_of_victory	strength_of_schedule	simple_rating	offensive_ranking	defensive_ranking	playoffs	sb_winner
Miami	Dolphins	2000	11	5	323	226	97	6.1	1.0	7.1	0.0	7.1	Playoffs	No Superbowl
Indianapolis	Colts	2000	10	6	429	326	103	6.4	1.5	7.9	7.1	0.8	Playoffs	No Superbowl
New York	Jets	2000	9	7	321	321	0	0.0	3.5	3.5	1.4	2.2	No Playoffs	No Superbowl
Buffalo	Bills	2000	8	8	315	350	-35	-2.2	2.2	0.0	0.5	-0.5	No Playoffs	No Superbowl
New England	Patriots	2000	5	11	276	338	-62	-3.9	1.4	-2.5	-2.7	0.2	No Playoffs	No Superbowl
Tennessee	Titans	2000	13	3	346	191	155	9.7	-1.3	8.3	1.5	6.8	Playoffs	No Superbowl

standings %>% 
  skim()

Data summary
Name	Piped data
Number of rows	638
Number of columns	15
_______________________
Column type frequency:
character	4
numeric	11
________________________
Group variables	None

Variable type: character

skim_variable	complete_rate	min	max	n_unique
team	1	5	13	32
team_name	1	4	10	32
playoffs	1	8	11	2
sb_winner	1	12	13	2

Variable type: numeric

skim_variable	complete_rate	mean	sd	p0	p25	p50	p75	p100	hist
year	1	2009.53	5.76	2000.0	2005.00	2010.0	2014.75	2019.0	▇▇▇▇▇
wins	1	7.98	3.08	0.0	6.00	8.0	10.00	16.0	▂▆▇▆▂
loss	1	7.98	3.08	0.0	6.00	8.0	10.00	16.0	▂▆▇▆▂
points_for	1	350.28	71.40	161.0	299.00	348.0	396.00	606.0	▂▇▇▂▁
points_against	1	350.28	59.55	165.0	310.00	347.0	391.50	517.0	▁▃▇▆▁
points_differential	1	0.00	101.09	-261.0	-75.00	1.5	72.75	315.0	▂▆▇▅▁
margin_of_victory	1	0.00	6.32	-16.3	-4.70	0.1	4.57	19.7	▂▆▇▅▁
strength_of_schedule	1	0.00	1.63	-4.6	-1.10	0.0	1.20	4.3	▁▅▇▅▁
simple_rating	1	0.00	6.20	-17.4	-4.47	0.0	4.50	20.1	▁▆▇▅▁
offensive_ranking	1	0.00	4.34	-11.7	-3.18	0.0	2.70	15.9	▁▇▇▂▁
defensive_ranking	1	0.00	3.57	-9.8	-2.40	0.1	2.50	9.8	▁▅▇▅▁

So, look at this snapshot of the data, there seems to be all kinds of interesting statistics between attendance and what appears to be by team year statistics.

The games dataset

kable(head(games))

year	week	home_team	away_team	winner	tie	day	date	time	pts_win	pts_loss	yds_win	turnovers_win	yds_loss	turnovers_loss	home_team_name	home_team_city	away_team_name	away_team_city
2000	1	Minnesota Vikings	Chicago Bears	Minnesota Vikings	NA	Sun	September 3	13:00:00	30	27	374	1	425	1	Vikings	Minnesota	Bears	Chicago
2000	1	Kansas City Chiefs	Indianapolis Colts	Indianapolis Colts	NA	Sun	September 3	13:00:00	27	14	386	2	280	1	Chiefs	Kansas City	Colts	Indianapolis
2000	1	Washington Redskins	Carolina Panthers	Washington Redskins	NA	Sun	September 3	13:01:00	20	17	396	0	236	1	Redskins	Washington	Panthers	Carolina
2000	1	Atlanta Falcons	San Francisco 49ers	Atlanta Falcons	NA	Sun	September 3	13:02:00	36	28	359	1	339	1	Falcons	Atlanta	49ers	San Francisco
2000	1	Pittsburgh Steelers	Baltimore Ravens	Baltimore Ravens	NA	Sun	September 3	13:02:00	16	0	336	0	223	1	Steelers	Pittsburgh	Ravens	Baltimore
2000	1	Cleveland Browns	Jacksonville Jaguars	Jacksonville Jaguars	NA	Sun	September 3	13:02:00	27	7	398	0	249	1	Browns	Cleveland	Jaguars	Jacksonville

From this vantage, it looks like I could connect the team name from the attendance data to the home team of the games data. To do so, I’ll have to make a key that matches. Most readily, it looks like I’ll need to combine a few the ‘team’ and ‘team_name’ columns in the attendance data.

att_reshape <- attendance %>% 
  mutate(t_name = str_c(team, team_name, sep = " ")) %>%
  select(-team, -team_name)

# to merge these datasets, I needed 'week' to be numeric on both... 
# and for whatever reason it was a character field to begin with...
games <- games %>%
  mutate(week = as.numeric(week))

att_games <- left_join(att_reshape, games, 
                       by = c('t_name' = 'home_team', 'year' = 'year', 'week' = 'week'))

kable(head(att_games))

year	total	home	away	week	weekly_attendance	t_name	away_team	winner	tie	day	date	time	pts_win	pts_loss	yds_win	turnovers_win	yds_loss	turnovers_loss	home_team_name	home_team_city	away_team_name	away_team_city
2000	893926	387475	506451	1	77434	Arizona Cardinals	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
2000	893926	387475	506451	2	66009	Arizona Cardinals	Dallas Cowboys	Arizona Cardinals	NA	Sun	September 10	20:35:00	32	31	322	1	330	2	Cardinals	Arizona	Cowboys	Dallas
2000	893926	387475	506451	3	NA	Arizona Cardinals	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
2000	893926	387475	506451	4	71801	Arizona Cardinals	Green Bay Packers	Green Bay Packers	NA	Sun	September 24	16:06:00	29	3	455	1	209	4	Cardinals	Arizona	Packers	Green Bay
2000	893926	387475	506451	5	66985	Arizona Cardinals	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
2000	893926	387475	506451	6	44296	Arizona Cardinals	Cleveland Browns	Arizona Cardinals	NA	Sun	October 8	16:15:00	29	21	315	2	240	0	Cardinals	Arizona	Browns	Cleveland

At first glance it looks like there is a bunch of missing data, but because I merged on the home team, almost all the missingness appears to be related to the team is away or if they had a by week. Which makes it less alarming… I was alarmed at first… “did my join work?”

Nevertheless, I think we’re almost at a point to start visualizing stuff. It would be helpful to have a column identifying if a team is home or away… just so I can sort on it later.

att_games_ha <- att_games %>%
  mutate(away_team_ind = if_else(is.na(away_team) & !is.na(weekly_attendance), 1, 0),
         away_team_ind = case_when(
           is.na(weekly_attendance) ~ 9999,
           TRUE ~ away_team_ind))

So, by doing all of this, I can see trends across time of how well a team does in terms of attendance between home and away games.

Lets take a look.

chiefs <- att_games_ha %>%
  filter(t_name == "Kansas City Chiefs") 

chiefs_gg <- chiefs %>%
  filter(away_team_ind != 9999) %>%
  group_by(year, week, away_team_ind) %>%
  summarize(average_att = mean(weekly_attendance)) %>%
  ggplot(aes(x = year, y = average_att)) +
  geom_point() + 
  facet_wrap(~away_team_ind)

chiefs_gg

Well, that’s interesting… but I wonder if the obvious dip in at home attendance between ~2007 and ~2013 is simply a localized artifact to the Chiefs.

all_gg <- att_games_ha %>%
  filter(away_team_ind != 9999) %>%
  group_by(t_name, year, away_team_ind) %>%
  summarize(average_att = mean(weekly_attendance)) %>% ungroup() %>%
  ggplot(aes(x = year, y = average_att, color = as.factor(away_team_ind))) +
  geom_point() + 
  facet_wrap(~t_name) + 
  theme(legend.position = "top")

all_gg

So obviously, each team has a fairly unique pattern of attendance, especially between home and away games. You can also see where some teams got a new stadium that pushed attendance up, such as the Dallas Cowboys.

gg1 <- att_games_ha %>%
  filter(away_team_ind != 9999) %>%
  group_by(t_name, year, week, away_team_ind) %>%
  summarize(average_att = mean(weekly_attendance)) %>%
  ggplot(aes(t_name, average_att, color = as.factor(away_team_ind))) +
  geom_boxplot(outlier.alpha = .5) + 
  coord_flip() + 
  theme(legend.position = "top")

gg1

Although both the previous graph do not exhibit any clear reoccuring or dicernable trends, it makes me wonder what the relationship between home attendance and season performance is. Said another way, does a strong home team crowd during the first half of the season, relate to eventual success?

Lets take a look.

standings <- standings %>%
  mutate(t_name = str_c(team, team_name, sep = " "))
  
predict_1 <- att_games_ha %>%
  filter(!is.na(away_team),
         week < 8) %>%
  group_by(year, t_name) %>%
  summarize(avg.att = mean(weekly_attendance)) %>% ungroup() %>%
  left_join(standings, by = c("year", "t_name")) %>%
  mutate(perc.win = wins/(wins+loss))

cor(predict_1$avg.att, predict_1$perc.win) #this is not promissing, but lets visualize

## [1] 0.09888602

predict_1_gg <- predict_1 %>%
  ggplot(aes(x = perc.win, y = avg.att)) + 
  geom_point() 

predict_1_gg

So much variability. I would assume this is because each team has different stadium sizes, and therefore the y-axis is not relative across teams. Lets see if we can control this.

Let’s first create a function to normalize data within group (year, team)

zscore <- function(m){
  (m - mean(m)) / sd(m)
}

Group it and then lets see how things relate.

# Full season results were used, although home and away games' attendance will count for more than one team at a time. 

predict_2 <- att_games_ha %>%
  # filter(!is.na(away_team)) %>%
  filter(!is.na(weekly_attendance)) %>%
  group_by(year, t_name) %>%
  mutate(avg.att = zscore(weekly_attendance)) %>% ungroup() %>%
  left_join(standings, by = c("year", "t_name")) %>%
  mutate(perc.win = wins/(wins+loss)) %>%
  # filter(week < 8) %>%
  # filter(week > 4 & week < 10) %>% #trying out different perspectives
  # filter(week > 8) %>%
  group_by(year, t_name, perc.win) %>%
  summarize(avg_first_half = mean(avg.att)) %>% ungroup()

Lets take a look now.

predict_2_gg <- predict_2 %>%
  ggplot(aes(x = perc.win, y = avg_first_half)) + 
  geom_point() + 
  geom_smooth(method = "auto")
  
  # geom_point() + 
  # geom_smooth(stat = "smooth")

predict_2_gg

Although first half season attendance does not seem to be extensively predictive, perhaps there are other indicators that could help improve this model. Lets look a bit deeper here.

cor(predict_2$perc.win, predict_2$avg_first_half, method = "pearson")

## [1] -0.2012417

lm1 <- lm(data = predict_2, perc.win ~ avg_first_half)
broom::tidy(lm1)

## # A tibble: 2 x 5
##   term           estimate std.error statistic   p.value
##   <chr>             <dbl>     <dbl>     <dbl>     <dbl>
## 1 (Intercept)       0.506   0.00757     66.8  8.91e-290
## 2 avg_first_half   -0.136   0.0263      -5.18 2.97e-  7

broom::glance(lm1)

## # A tibble: 1 x 11
##   r.squared adj.r.squared sigma statistic p.value    df logLik   AIC   BIC
##       <dbl>         <dbl> <dbl>     <dbl>   <dbl> <int>  <dbl> <dbl> <dbl>
## 1    0.0405        0.0390 0.189      26.8 2.97e-7     2   158. -311. -298.
## # … with 2 more variables: deviance <dbl>, df.residual <int>

lm2 <- lm(data = predict_2, perc.win ~ year + avg_first_half + year*avg_first_half)
broom::tidy(lm2)

## # A tibble: 4 x 5
##   term                 estimate std.error statistic p.value
##   <chr>                   <dbl>     <dbl>     <dbl>   <dbl>
## 1 (Intercept)          8.43e- 1  2.70e+ 0     0.312   0.755
## 2 year                -1.70e- 4  1.34e- 3    -0.126   0.899
## 3 avg_first_half       1.15e+17  2.34e+17     0.491   0.624
## 4 year:avg_first_half -5.67e+13  1.16e+14    -0.487   0.626

broom::glance(lm2)

## # A tibble: 1 x 11
##   r.squared adj.r.squared sigma statistic p.value    df logLik   AIC   BIC
##       <dbl>         <dbl> <dbl>     <dbl>   <dbl> <int>  <dbl> <dbl> <dbl>
## 1   0.00325      -0.00147 0.193     0.689   0.559     4   146. -283. -260.
## # … with 2 more variables: deviance <dbl>, df.residual <int>

predict_3 <- predict_2 %>%
  left_join(standings, by = c("year", "t_name"))

lm3 <- lm(data = predict_3, perc.win ~ year + avg_first_half + points_for)
broom::tidy(lm3)

## # A tibble: 4 x 5
##   term            estimate std.error statistic   p.value
##   <chr>              <dbl>     <dbl>     <dbl>     <dbl>
## 1 (Intercept)     8.60e+ 0  1.81e+ 0      4.75 2.55e-  6
## 2 year           -4.39e- 3  9.04e- 4     -4.85 1.53e-  6
## 3 avg_first_half  4.38e+14  4.26e+14      1.03 3.04e-  1
## 4 points_for      2.03e- 3  7.29e- 5     27.9  2.68e-112

broom::glance(lm3)

## # A tibble: 1 x 11
##   r.squared adj.r.squared sigma statistic   p.value    df logLik   AIC   BIC
##       <dbl>         <dbl> <dbl>     <dbl>     <dbl> <int>  <dbl> <dbl> <dbl>
## 1     0.552         0.550 0.129      261. 3.77e-110     4   402. -793. -771.
## # … with 2 more variables: deviance <dbl>, df.residual <int>

tidytuesday - NFL Data - Week 6

MLDL

2/6/2020

The attendance dataset

The standings dataset

The games dataset